Alkylthiosulfates (R—S—SO3−Na+), known as Bunte salts, have been known for a long time [Bunte, H. Chem. Bet. 1874, 7, 646]. These salts are readily prepared by reacting alkylhalides with sodium thiosulfate. Extensive reviews on the preparation and classical reactions of Bunte salts have appeared in the literature (for example, Milligan, B.; Swan, J. M. Rev. Pure Appl. Chem. 1962, 12, 72).
Much of the useful chemistry of Bunte salts results from the potential of the sulfite moiety to leave the molecule. Small molecule Bunte salts have various uses. For instance they can be used as insecticides or fungicides, radiation protecting agents (for example as described in U.S. Pat. No. 5,427,868 of Bringley et al.), and paint additives.
Polymeric Bunte salts and Bunte salt derivatives have been used for setting hair as described in U.S. Pat. No. 5,071,641 (Lewis) and U.S. Pat. No. 5,424,062 (Schwan et al.).
Water-soluble polymers formed from thiosulfate salts are useful in a variety of applications including their use to crosslink or otherwise modify the properties of natural materials such as wool fibers, cellulosic fibers, and leathers, and as water-insoluble polymeric sulfur dyes. These water-soluble polymers are also used in the coating industry.
Bunte salts are commonly reduced to corresponding thiols either by decomposition with mineral acids or by treatment with reducing agents such as NaBH4, dithioerythritol, or mercaptoethanol. In addition, Bunte salts can be decomposed to disulfides at moderate temperatures. In solid state, Bunte salts are known to decompose upon heating to form disulfides, a feature that has been used as thermally switchable imaging materials in printing plates. By “switchable” is meant that the polymer is rendered from hydrophilic to relatively more hydrophobic, or from hydrophilic to relatively more hydrophobic, upon exposure to heat. For example, U.S. Pat. No. 5,985,514 (Zheng et al.) and U.S. Pat. No. 6,465,152 (DoMinh et al.) describe lithographic printing plate precursors that are composed of thiosulfate containing polymers, which upon exposure to IR radiation are crosslink as the thiosulfate groups are decomposed.
Bunte salts can be used to synthesize disulfides by oxidation [Affleck, J. G.; Dougherty, G. J. Org. Chem. 1950, 15, 865. and Milligan, B. L.; Swan, L. M. J. Chem. Soc. 1962, 2172], acidic hydrolysis [Kice, J. L. J. Org. Chem. 1963, 28, 957], or alkaline degradation [Alonso, M. E.; Aragona, H. Org. Synth. 1978, 58, 147]. Disulfides also can be formed from Bunte salts electrochemically [Czerwinski, A.; Orzeszko, A.; Kazimierczuk, Z.; Marassi, R.; Zamponi, S. Anal. Lett. 1997, 30, 2391]. This method has been extended to form polydisulfides from “double” Bunte salts, that is, molecules carrying two thiosulfate groups, using electrochemistry with gold electrodes [Nann, T.; Urban, G. A. J. Electroanal. Chem., 2001, 505, 125].
In all these noted methods, the Bunte salts are either decomposed by heating or electrochemically in solution, or at high pH. No efficient photochemical method to decompose Bunte salts is known. More specifically, a simple method for patterning thin films using Bunte salt polymers is not known and would be desirable for various purposes.
It would be very desirable to decompose Bunte salts by photochemical means, or by using a photochemical electron transfer process (also known as photoinduced electron transfer).